The Porelon Universal Twin Spool Compatible Calculator Ribbon replaces manufactures part #'s M-310, RB-2, 013091. This ribbon provides vivid and consistent black and red color in addition to exceptional light fastness and durable impressions. This product has been designed and manufactured to operate the original equipment identified. 1 pack. Porelon specializes in creating inking products and elastomers for a wide variety of industries. They focus their scientific, engineering and customer service efforts on delivering solutions that perform to your exact specifications.